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How to Avoid Fog on Your Windshield

Published: August 31, 2018

Picture this. You’re driving down the road when seemingly out of nowhere your windshield begins to fog up. Annoyed and frustrated, you do everything you can to fix the problem. You’ve frantically hit all of the climate control buttons and cranked up your windshield wipers but you’re still at a loss. We’ve all been there. A foggy windshield situation is not only incredibly frustrating but it is also very dangerous to you and other drivers. That’s why we’ve compiled this article to help you learn about the causes of foggy windows and how to prevent window fog in your vehicle altogether.

How Fog Forms

In order to understand how to get rid of and prevent foggy auto glass, we must first discuss why and how the fog is forming on your windshield and/or windows. Fog on either the inside or outside of the windows of your vehicle is caused by differences in humidity. For example, if you get into your car on a cold winter day, the relative humidity is low outside of your vehicle due to the low temperature. Once you enter your vehicle, the humidity inside the car immediately begins to rise as you breathe out air that is roughly 100% humidity. This causes fog to form on the inside of your windows and windshield.

Your breath isn’t the only thing that can cause foggy windows. If you’re returning from a workout or a day at the pool, then the moisture from your body evaporating into the air can cause an increase in humidity inside of the vehicle. Sometimes, tracking in water on your shoes from dewy grass or even spilling a small amount of liquid in your cup holder can cause a spike in humidity as well.

At times, you may realize that the fog is not on the inside of your windshield, but rather on the outside of your vehicle. That’s often the case when driving through a very hot and humid area. In this instance, the humidity outside of your vehicle is much higher and the temperature is likely much warmer than in your air conditioned car.

How to Get Rid of Fog on A Windshield or Window

One of the best and easiest ways to get rid of fog is to balance out the humidity between the air on the interior and exterior of your car. Sometimes doing this is easier said than done. For example, on a very cold winter day, when your breath alone is enough to raise the humidity of the air in your car to 100%, you may be tempted to crank up the heat and defrost and hope that does the trick. While that certainly may help, you’ll also want to take another step that may seem a little counter-intuitive. Since warmer air can hold more moisture than colder air, adding hot air to your vehicle alone might actually worsen the problem. Therefore, you’ll want to turn the heat up high, turn the defrost setting on, and turn on the air conditioning setting. Even if your temperature setting is all the way up, the air conditioner setting can still be activated.

Turning on your air conditioner in the freezing cold weather may not seem like the best idea, but with the heat setting on high, the air will not get as cool as you’d expect. While it may cool some of the air, overall the airflow will remain warm. The air conditioner in your vehicle is not only designed to cool off warm air, but it also removes the humidity from it. Therefore, when the humidity inside of your vehicle is much higher than the humidity outside and there’s fog on the inside of your windshield or windows, crank up the air conditioning and defroster on both the front and rear window. You’ll be surprised how fast the fog begins to evaporate.

In the case of fog on the outside of your vehicle on a warm and humid day, you’ll want to try something a bit different. You may want to try turning off your air conditioning for a moment, rolling down the windows and letting the humidity and air temperature balance out in order to remove fog on the outside of your windshield. If it’s simply too hot, you may have to drive with your windshield wipers on and limit the amount of cool air that is flowing directly toward your windshield. In this case, we advise not using the defrost setting on your car as it will push more cool air directly onto the windshield, causing more fog on the outside and further inhibiting your vision.

How to Prevent it Altogether

One of the easiest ways to prevent foggy windows in your vehicle is to turn off the climate control “recirculation” button. This button is standard in most vehicles, and looks like a car with a looped arrow inside. Basically, when this function is turned on, your vehicle will circulate air within the vehicle and cool and/or heat the air that is already inside. Many times, this inhibits changes in humidity. If this setting is turned off, your vehicle will draw air in from the outside, push it through a filter and then begin to cool and/or heat it, allowing for an easier balance between the interior and exterior air humidity.

Another way to ensure that your windshield and windows stay clear is to keep them clean and to clean them the correct way. Many products can leave a residue on your windshield or windows, causing them to be more prone to collecting moisture because there is already a film on the glass surface. Many recommend Armor All Glass Cleaner as the best way to ensure that you are getting a good clean surface without leaving any residue. We also recommend using a durable paper towel or clean microfiber cloth to ensure that there is no dust or residue left behind.

A third and final way to keep your windows from fogging up is to leave them cracked whenever you park. This is best done if you have a garage or covered carport or if you are parked in a safe area and you know there will not be any rain in the forecast. By leaving your windows slightly cracked when the car is not on, the humidity inside the vehicle will naturally reach an equilibrium with the humidity outside allowing for you to hop in, turn the key and get moving without a foggy window in sight!

We understand that windshield and window fog is incredibly frustrating. For more information about caring for the glass surfaces in your vehicle, or to discuss our auto glass repair and replacement services, contact Smiley’s Glass by dialing (804) 320-7172.